S-amidomethylidene dithiophosphoric acid triesters



Patented Aug. 28,1951

S-AMIDOMETHYLIDENE DITHIOPHOS- PHORIC ACID TRIESTERS Edwin 0. Hook, OldGreenwich, Conn., and Philip H. Moss, Austin, Tex., assignors toAmerican Cyanamid Company, New York, N. Y., acorporation of Maine NoDrawing. Application June 3, 1950, Serial No. 166,061

This invention relates to S-amidomethylidene dithiophosphoric acidtriesters and to their methods of preparation. The invention includesthe novel dithiophosphoric acid triesters themselves, methods forpreparing them and hydrocarbon oil compositions containing them.

We have discovered a novel class of dithiophosphoric acid triesterswhich, we have found, are excellent antioxidants for hydrocarbon oils.These new compounds are S-amidomethylidene dithiophosphoric acidtriesters of the formula in which R is an aliphatic hydrocarbon radicalof 1-18 carbon atoms and R and R are aliphatic, cycloaliphatic oraromatic hydrocarbon radicals. These compounds are prepared bycondensing an 0,0-diester of dithiophosphoric acid with a reactivealiphatic carxoylic acid amideand with formaldehyde, or with themethylol derivative that is obtained by first condensing formaldehydewith an amide of an aliphatic carboxylic acid.

The 0,0-diesters of dithiophosphoric acid are well known compounds, andare usually prepared by condensing alcohols or phenols with phosphoruspentasulfide. Any such 0,0-diester of dithiophosphoric acid may be usedin preparing the new compounds of our invention, including the0,0-dialiphatic dithiophosphoric acid diesters, the 0,0-diaryldithiophosphoric acid diesters and the dicycloaliphatic dithiophosphoricacid diesters. However, when compounds having a relatively highpercentage of combined phosphorus and sulfur are desired, as in theproduction of lubricating oil antioxidants having a high activity atrelatively low temperatures which is sometimes required in turbine oilsand anticorrosion oils, it is preferably to employ an 0,0- dialkyldithiophosphoric acid in which the alkyl groups are of relatively lowmolecular weight, such as those containing from 1 to about 8 carbonatoms. Dialkyl dithiophosphoric acids of higher molecular weight may ofcourse be employed, such as the didecyl, didodecyl, ditetradecyl ordioctadecyl dithiophosphoric acids. Typical dicycloalkyldithiophosphoric acid esters which may be used are those obtained by thecatalytic hydrogenation of naphthenic acids to the correspondingalcohols and include the 0,0-dicyclohexyl, methyl cyclopentenyl andsimilar alcohol esters. The 0,0-dia1kylphenyl dithiophosphoric aciddiesters such as the 4-butyl-, -4-'a-myl- 6 Claims. (Cl. 260-461) and4-octylphenyl diesters may also be employed.

Although any carboxylic acid amide may be used, we prefer to employ thealiphatic carbcxylic acid monoamides of the formula R.CO.NH2

in which R is an aliphatic hydrocarbon radical of 1-18 carbon atoms. Forthe purpose of obtaining a relatively high percentage of phosphorus andsulfur in the hydrocarbon oil, We usually employ acid amides of thistype in which R, is an aliphatic radical of 1-4 carbon atoms; i. e.,acct.- amide, propionamide, .butyramide, acrylamide, methyl acrylamideand the like. However, in cases where a higher degree of solubility inhydrocarbon oils of lubricating grade may be desirable, 'we can ofcourse employ the amides of higher fatty acids such as those of 8-18carbon atoms including lauramide, myristamide, palmitamide, stearamideand the like.

The reaction whereby our new compounds are formed is carried out simplyby mixing the above two classes of compounds with formaldehyde or with aformaldehyde-yielding substance such as paraformaldehyde, trioxymethylene or the like. The reaction can be carried out at any suitabletemperature from room temperature to 100 C. or higher; however, in mostcases it is preferable to employ temperatures between room temperatureand about C. in order to avoid loss of sulfur from the dithiophosphoricacid diester by excessive evolution of hydrogen sulfide during thereaction. If desired the formaldehyde may first be reacted with thecarboxylic acid amide to form the corresponding methylol derivative,which is then condensed with the O;O-dithioph0sphoric acid diester. Itis unnecessary to maintain any particular ratio of reacting ingredients,as the three reagents condense in equimolecular ratios; in fact, it issometimes advantageous to employ an excessive quantity of the acid amideto function as a diluent for the reaction mixture. Of course,non-reactive diluents may be employed such as volatile hydrocarbons ofthe type of henzene, toluene, solvent naphtha, chlorinated hydrocarbonsand the like.

The products obtained by this reaction vary from light colored tanliquids to dark brown, amorphous solids, depending on their molecularweight. Thus, when 0,0-dialkyl dithiophosphoric acids in which the alkylgroups are hydrocarbon radicals of from l to about 8 carbon atoms areused together with lower aliphatic amides such as acetamide,propionamide and the like, the products are --tan liquids that areinsoluble in water but soluble in hydrocarbon solvents. When aliphaticmonocarboxylic acid amides of higher molecular weight are employed, suchas lauramide or 'stearamide, the products are waxlike solids that arereadily soluble in both paraffin base and Mid Continent base lubricatingoils.

The novel products of the present invention are preferably used inlubricating oils in relatively small quantities which may vary fromabout 0.1% up to about 4-5% or greater, depending on the particular oiland on the degree of protection desired therein. In automobile enginelubricating oils, quantities on the order of 0.2% to 2-3% are usuallyincorporated into the oil. Our novel antioxidants are compatible withall of the commonly used detergents, stabilizers, sludge-inhibitors andother ingredients of compounded oils and may be used in conjunction withsmaller or larger quantities of aliphatic or aromatic sulfonates such ascalcium petronate, alkyl phenol sulfides such as p,p-dibutyl-, diamylordioctyl phenol monoor polysulfides and their polyvalent metal salts,2,4-dialkyl phenol monoor polysulfides and their-metal salts, or saltsof oxygenor sulfur-containing acids of phosphorus such as thosedescribed in U. S. Patents Nos. 2,364,284 and 2,228,658 and Reissue22,829. These and other additives are usually employed in the oils inquantities of about 0.l5%, most commonly in quantities of about 0-.52%,in admixture with the antioxidants of the present invention.

The invention will be further illustrated in detail by the followingspecific examples. It should be understood, however, that although theseexamples may describe in detail some of the specific compounds of theinvention, they are given also for purposes of illustration and theinvention in its broader aspects is not limited thereto. In theseexamples the products are evaluated as lubricating oil antioxidantsbydisw solving a portion in an SAE. Mid-Continent base lubricating oiltogether with 0.04% of iron naphthenate, based on the F8203 equivalent,and subjecting the oil to the Underwood oxidation test. .In this test1500 cc. of the oil is heated for 10 hours at 325 F. in an opencontainer providing free. circulation of air while portions of the oilare sprayed continuously against two freshly sanded alloy bearings. Whensilver-cadmium alloy bearings were used in the test with the above oilcontaining the iron naphthenate oxidation catalyst but no antioxidantthe loss in weight due to corrosion was 1097 mg.

Eazample 1 A mixture of 50 grams of 0,0-diethy1 dithiophosphoric acidand 14 grams of acetamide was agitated while 19 grams of 37% aqueousformaldehyde solution were added with stirring. Agitation was continuedat room temperature for 2 -days, after which time the condensationproduct was dissolved in benzene and washed with water. The product wasthen washed with an aqueous 1% solution of sodium carbonate, againwashed with water, and dried. After removal of the benzene by vacuumdistillation there remained 39 grams of a light-colored mobile liquid.The product was soluble in a Mid- Continent base lubricating oil of SAE30 grade and was tested in this oil at 0.5% concentration by theUnderwood oxidation test using silvercadmium bearings. There was no lossin weight of the bearings after the test, indicating that theproduct-was an effective, antioxidantmr the. 91

Example 2 A portion of distilled diethyl dithiophosphoric acid (N. E.202) weighing 41 grams was agitated while 40 grams of 57.8% methylolacrylamide was introduced slowly. The reaction vessel was cooled on anice bath as there was considerable evolution of heat during the earlystages of this addition. The mixture was stirred for 5 hours and at theend of that time had become an opaque thick liquid. It was allowed tostand overnight and separated into two layers. Water and benzene wereadded and the water layer was separated and discarded. The benzene layerwas washed with water, dried over calcium sulfate and freed of benzeneunder reduced pressure. There was obtained 51 grams of a dark, thickliquid that was free of hydrogen sulfide odor.

The product was tested in Mid-Continent base SAE 30 lubricating oil at aconcentration of 0.5% by the Underwood oxidation test againstsilvercadmium bearings. There was no bearing corrosion at the end of thetest.

Example 3 One-fourth mol (15 grams) of acetamide was stirred into 10 cc.of water containing 0.2 gram of potassium carbonate. To this solutionwas added 24 grams (0.3 mol) of 37% aqueous formaldehyde solution andthe liquid was stirred for 3 hours. There was then added 65 grams (0.25mol) of diisobutyl dithiophosphoric acid (N. E. 260) and stirring wascontinued for 4 hours. The mixture was then allowed to stand overnight.The aqueous layer was then discarded and the hydro- 1 gen sulfide-freelower layer was washed with water and freed of volatile matter byheating it at reduced pressure at C. There was obtained 79 grams of atan colored liquid having a pleasant odor and good solubility inhydrocarbon lubricating oils.

The product was tested by the Underwood oxidation test againstsilver-cadmium bearings at a concentration of 0.5%. At the end of thetest the bearing loss was 3 milligrams.

Example 4 A solution of 31.6 grams (0.1 mol) of crude di(methylisobutylcarbinyl) dithiophosphoric acid and 6 grams of acetamidein 40 grams of ethanol was heated to 50 C. and agitated while 10 gramsof 37% aqueous formaldehyde was added. The agitation was continued whilethe mixture cooled to room temperature after which the mixture wasallowed to stand overnight. It was then washed with water and strippedof volatile material by heating at reduced pressure. The product, a darkbrown liquid free of hydrogen sulfide odor, was tested at 0.5%concentration in SAE 30 Mid-Continent base lubricating oil by theUnderwood oxidation test against silver-cadmium bearings. The bearingloss at the end of the test was 6 milligrams.

Example 5 A solution of 25 grams (0.55 mol) of technical formamide and48 grams (0.59 mol) of 37% formalin containing 0.2 gram of potassiumcarbonate was stirred for 1 /2 hours. This reaction was very slightlyexothermic. 130 grams (0.5 mol) of crude diisobutyl dithiophosphoricacid (N. E. 260) was added and the solution stirred for 6' hours. Thisreaction was very mildly exothermic. By washing with water, drying andstripping the liquid there was obtained grams q fi r' The product, alight-colored oil free of hydrogen sulfide, was found to possess goodsolubility in hydrocarbon lubricating oils. It was tested inMid-Continent oil of SAE 30 grade at a concen tration of 0.5% againstsilver-cadmium bearings. There was no bearing loss at the end of thetest.

Example 6 A solution of 31.3 grams (0.1 mol) of methyl olstearamide in110 cc. of ethyl alcohol was heated to 45 C. and agitated while 18.6grams of diethyl dithiophosphoric acid were added. Agitation wascontinued at the same temperature for 4 hours after which the mass wasallowed to stand at room temperature for two days. It was then dilutedwith benzene and washed with water containing a little sodium dioctylsulfosuccinate, and stripped of volatile material by heating on a steambath at reduced pressure. The product was a light tan waxy solid thatwas easily soluble in lubricating oil.

The product was tested in a Mid-Continent base SAE 30 lubricating oil at1% concentration against silver-cadmium bearings. The bearing loss atthe end of the test was milligrams.

Example 7 In cases where a higher percentage of sulfur in the oil isdesired thioamides may be employed. Thus, for example,N-(0,0-di-n-propyl dithiophosphato methyl) thioacetamide was prepared bythe following procedure:

A solution of 19 grams (0.25 mol) of thioacetamide in 70 cc. of ethylalcohol was prepared and 0.4 gram of potassium carbonate in 4 cc. ofwater was added. This solution was stirred as 24 grams (0.3 mol) of 37%aqueous formaldehyde solution was poured in. After 90 minutes there wasadded 59 grams (0.25 mol) of distilled di-n-propyl dithiophosphoricacid, whereupon a clear, colorless solution was obtained. This wasallowed to stand at room temperature for 2 days after which it waswashed three times with water and then stripped of volatile material byheating at reduced pressure on a steam bath. There was obtained '76grams of an almost colorless liquid that was free from hydrogen sulfide.It was tested at 0.5% concentration in a Mid-Continent base SAE 30lubricating oil against silver-cadmium bearings. 6 milligrams.

What we claim is:

1. Triesters of dithiophosphoric acid of the formula At the end of thetest the bearing loss was 6 in which each of R, R and R is an aliphatichydrocarbon radical of 1-18 carbon atoms.

2. Triesters of dithiophosphoric acid of the formula P oH3.o0.NB.oH2.s\OR1 in which each of R and R is an aliphatic hydrocarbon radical of1-18 carbon atoms.

3. A triester of dithiophosphoric acid having the formulaCH:.CO.NH.CH2,S/ \OC2H5 4. A triester of dithiophosphoric acid havingthe formula 5. A triester of dithiophosphoric acid having the formulaCHs.CO.NH.CH2.S 004m 6. A method of preparing a dithiophosphoric acidtriester of the formula in which each of R, R and R is an aliphaticradical of 1-18 carbon atoms which comprises mixing together an0,0-dialkyl dithiophosphoric acid in which each alkyl radical containsfrom 1 to 18 carbon atoms, an acid amide of the formula R.CO.NH2

in which R is an aliphatic hydrocarbon radical of 1-18 carbon atoms, andformaldehyde and allowing the mixture to react at a temperature betweenroom temperature and about C. until a dithiophosphoric acid triester isformed.

EDWIN O. HOOK. PHILIP H. MOSS.

No references cited.

1. TRIESTERS OF DITHIOPHOSPHORIC ACID OF THE FORMULA